All the microwaves I've had over the 25 years have had timer functions. I think there's only been one time I've accidentally set it cooking itself instead of using the timer, but luckily I realised what I'd done before any damage.

The last two or three (Panasonics) have had multi-stage timers, which I use all the time. So you can set it to beep after 3 minutes then after another 3 minutes if you're cooking steaks (three minutes per side) or 12 minutes+8 minutes for steaming rice (turn off after 12 mins). Set the timers all at once; don't have to reset it after the first stage, and I find it much quicker than using the phone's timer (long password!).