Cybersecurity Basics:
Protect Smart Phones and Tablets

Set up a strong PIN for identifying yourself when you talk to your provider. There is a form of attack where the criminals transfer your phone to a different provider. That's the first step in taking over your number, so they can convince your bank that they are you. The attack is called a "port-out" scam or "SIM swapping". Contact your provider and say you want to increase the security on your account. Here are specific carriers' advice for protection. Some, like Sprint, don't have much useful information on-line:
AT&T T-Mobile Verizon Sprint

Set up as long a PIN as you can, making it a random number that has nothing to do with your bank PIN or other authenticators. Use a password manager (details later) to generate and remember this for you. You shouldn't need to use it very often.

Set up a screen lock. Use a PIN, 8 digits if your phone supports it. Don't do this with a pattern you draw with your finger, that's the weakest form available! Turn this on in the Settings menu on either Android or iPhone. Also require a second method,

Face recognition sounds fantastic, but so far it's only so-so in performance. It has significant error rates, both false reject (locking you out of your own phone) and false accept (allowing access to someone else because they're "close enough").

Fingerprint recognition seems to be better, although arguments persist about the relative security of face versus fingerprint. An increasing percentage of phones include an in-screen fingerprint reader.