Hacked iPhone after scammer call?

My family member recently fell for a scam, when they called a number claiming to be eBay support from their iPhone — but it actually was scammers that had them install the AnyDesk app (on a different device) and they ended up sending money to said scammers.

Now every time the iPhone is used to call a bank, credit card company, etc another incoming call happens immediately that appears to be scammers.

We’ve gotten rid of the AnyDesk app, searched the phone for other suspicious apps (and found none), updated software on the phone — and it still happens when any numbers are called for a financial institution.

If we backup the phone and do a factory reset, will we be backing up whatever it is that triggers the incoming calls? Or is a new phone and/or number the only fix?