How to create 2 Apple IDs on 1 iPhone

An individual Apple device can be used to create up to three new AppleID accounts - this limit existing to prevent account abuse.

While each device can create a maximum of three new AppleID accounts, outside of educational and corporate environments, you only sign-in to a single AppleID at any one time. Unlike some laptop and desktop computers with which you may be familiar, iPhone and iPad are essentially single-user devices; you cannot create multiple user profile/accounts - and switch between them.

And in addition to the correct information in the reply above, creating a new Apple ID will not bypass Activation Lock, if that is involved here. Some folks will try creating a new Apple ID to bypass Activation Lock, or will try resetting an iPhone to to bypass, and that won't work. Only the Apple ID and password holding the lock, or receipts or other proof of ownership sufficient to convince Apple will clear that lock.