You can probably do this using the stepup token
1. login via phone & otp
2. set a pin, using the password mechanism
3. do a stepup with this password (which will be very easy one, remove passwords restrictions
4. On app side, validate that this JWT is a stepup JWT
5. When it is expires, do the stepup with the password only
6. If user is not logged in, do OTP all over again
If you are using the password mechanism, then there is a reset option for it