Apple Care Plus

Yes, you usually can, you will pay for it separately from the phone.

Check in Settings / General / About, it will tell you how much time is left on the default limited warranty and if AC+ coverage is available. Note you only have 60 days after acquiring the phone to get AC+ on it.

Considering they let you pay for it monthly I’d guess yes, but you can read more about it

AppleCare Products - Apple