phase in

slowly start using something new over time

B2

What does "phase sth in" mean?

To phase something in means to introduce it gradually, in stages, rather than all at once. The idea is that there is a planned period of transition — things change step by step over weeks, months, or even years. This phrasal verb is typically used when a government, company, or institution wants to give people time to adapt to something new, such as a law, policy, or technology. It almost always appears with a time reference, such as 'over five years' or 'by 2030', because the gradual nature of the process is central to its meaning. You are most likely to encounter it in news articles, official documents, and business communications rather than in everyday conversation.

Examples

How to use it

subject + phase in + object (+ time frame)

The most common pattern, with an institutional subject introducing a policy, rule, or system over a stated period.

The government plans to phase in the new tax regulations over the next three years.

subject + phase + pronoun + in

When the object is a pronoun, it must go between 'phase' and 'in' — placing it after 'in' is not possible.

The board approved the new safety standards and decided to phase them in by the end of the decade.

object + be phased in (+ time frame)

The passive is very natural with this phrasal verb, especially in formal or official contexts describing how something is being implemented.

Stricter emissions targets will be phased in gradually to allow businesses time to comply.

subject + phase + short noun + in

Short noun phrases can be separated, placing the particle after the object.

The university decided to phase the new curriculum in ahead of the autumn term.

subject + phase in + long noun phrase

With longer or more complex noun phrases, it sounds more natural to keep the object directly after 'phase in' without separating.

The agency will phase in updated environmental protection standards before 2028.

Common Collocations

new regulationsa policychangesa taxreformsa system

Common Mistakes

Confusing 'phase in' with 'phase out'

'Phase in' means to gradually start using something new, while 'phase out' means to gradually stop using something that already exists. These are near-opposites, so using one when you mean the other completely reverses the meaning.

✗ The government will phase in the old licensing system by 2026.
✓ The government will phase in the new licensing system by 2026.
Wrong pronoun placement

When using a pronoun as the object, it must go between 'phase' and 'in'. Placing it after 'in' is ungrammatical in English.

✗ The company decided to phase in it gradually.
✓ The company decided to phase it in gradually.
Omitting the time frame or gradual element

'Phase in' inherently suggests a staged, gradual process, so it sounds most natural when paired with a time expression like 'over two years' or 'gradually'. Without this, the sentence can feel incomplete or unnatural, and a simpler verb like 'introduce' might be a better fit.

✗ The school will phase in the new grading system tomorrow.
✓ The school will phase in the new grading system over the coming semester.

Usage

This phrasal verb is mostly used in formal or semi-formal contexts like politics, business, and news. It almost always appears with a time expression like 'over the next five years' or 'gradually'.

Frequently Asked Questions

Can 'phase in' be used in the passive?

Yes, and the passive is actually very common with this phrasal verb. You will often see it in news reports and official documents. For example: 'The new requirements will be phased in over the next four years.' This structure is especially natural when the focus is on the policy or change rather than on who is introducing it.

Is 'phase in' formal? Can I use it in everyday conversation?

It leans towards formal and semi-formal use — you will see it most often in news articles, government announcements, and business communications. It is not wrong to use it in conversation, but it would sound a little official. In casual speech, people are more likely to say something like 'they're slowly introducing it' or 'it's being rolled out gradually'.

What kinds of things can be 'phased in'?

Typically, the object is something institutional or systemic — laws, regulations, taxes, policies, reforms, standards, or new technologies. The subject is usually an organisation, government, or company rather than an individual person. It would sound unusual to say someone 'phased in' a personal habit or daily routine.

What is the difference between 'phase in' and 'roll out'?

'Roll out' focuses on the deployment or launch of something, often across a wide area, and can imply speed or scale. 'Phase in' specifically emphasises that the introduction is gradual and staged over time. If something is happening slowly and in planned steps, 'phase in' is the more precise choice.

Can I use 'phase in' without saying when or how long the process takes?

Technically yes, but it sounds more natural and complete when a time reference is included, such as 'over three years', 'gradually', or 'by 2030'. Because the whole point of 'phase in' is that something happens slowly in stages, leaving out any time reference can make the sentence feel like it's missing important information.

Ready to practise?

Practise 1,000+ English phrasal verbs with interactive gap-fill exercises.

Start Practising →