Phone happens

So I go to work, put my phone on keylock, put it in my bag.

My shifts started at 2pm and finished at 6pm.

When I finish I find a miss call and a text from a random number: "Hi you rang me, I do not know who this is?"

So I check my call list and hey hey there is a outwards call to this number at 3:14pm.

Now when I finished my shift my phone was in the same place still on keylock.

No-one was in the staff room at 3:14pm, everyone was on the shop floor.

Any ideas?