All of this sounds feasible until we start to consider the technical details. How much power does a phone need to be be able to transmit to an overhead satellite? How does that compare with the power needed to transmit to a mast, a few tens of metres away?
There is a very big difference, which makes a very big difference to the size and usability of a mobile phone designed to do such a thing. It would need to be the masts on the ground which would have to be redesigned to maybe relay starlink bound transmissions. But then, if the mast exists, what would be the point of Starlink?