Normally, all Google accounts will receive 15GB of free storage for the owner to freely use to store emails, photos, videos and documents. The unlimited storage for Photos that was previously provided has been discontinued since June 1, 2021. But Google is now testing only providing 5GB of storage to new accounts. If the account owner wants to get 15GB of free storage, the user's phone number must be provided first.
This was noticed by u/sungusungu who shared his discovery on Reddit two days ago. This change in the terms of getting 15GB of storage has been done since March but has only just been noticed. Google has not yet released why the policy was changed without any notice.
It is most likely to ensure that only verified account owners can receive 15GB of storage. The technique of opening multiple Google accounts has been used for a long time to get free storage. Although Google One offers larger storage, not all users can afford the monthly subscription cost which is still quite expensive.

