I do the same, I strip the heads and the threads and its not my allen keys cause I've used brand new ones and it still strips lol also if the phoenix bolts are grade 8 then they're shit as fuck I had to change mine straight away. I stick washers on the stripped threads and just re tighten but just dont tighten excessively your scooter should still be dialed even if the bolts aren't tightened to the absolute max and if you strip the heads then that sucks just get new ones and avoid loosening and re tightening as much as possible.