I personally use my phone as a presence sensor with few problems, but I don’t have anything automatically open or unlock doors based on my presence. The closest thing I do is disarm SHM. I have a keyfob that I use to unlock the door before I get to it.
One thing I looked at doing was using the Wireless Sensor Tags as a backup presence device. Basically, the garage door or front door would only unlock automatically if both sensors showed present. I use a virtual presence sensor and a CoRE piston that adjusts based on the presence of both devices. Then I only use that virtual presence sensor in other automations. The problem I ran into was the stability of the tags, not the phone. You’re also adding another layer which makes it a little less dependable.
One thing I’ve proposed to ST is an auto presence sensor. Basically, something low power that runs off car battery power, has Z-Wave and/or wi-fi, and works as a presence sensor. That way you could, if you have multiple garage doors, have it automatically open the correct door based on which vehicle pulls up. It would also be useful in my example as a backup presence sensor.