I don’t see how it would be possible to use a cell phone to trigger such a device. If it were placed inside, the walls of the pressure cooker would act as a Faraday cage and block radio signals. If it were placed ouside, there would have to be wires running from the cell phone to the bomb inside the pressure cooker. The wires would compromise the seal and decrease the effectiveness of the pressure cooker in building up pressure immediately after detonation.
It’s been reported they believe these bombs were on timers, not remotely detonated.
Pressure cooker bombs were often used by ETA in Spain and also, iirc, by the IRA. It’s a technique lthst was taught in the PLO camps.
What you say is true but they could easily utilize an insulated feed-through in the pressure cooker to maintain the integrity of the vessel. It would have to be soldered or welded in.