Your bisectionF should be in bisectionF.m
Your f_feb15 should be in f_feb15.m
You should delete the "clear all" and you should never use it inside a function again. If you use "clear all" inside a script, it should be the very last thing in the script, and it should be a script dedicated to trying to get your MATLAB session unstuck. "clear all" is the "blow EVERYTHING up, especially yourself" command.
[r, iters] = bisectionF('f_feb15(x)', -2, .1)
[r, iters] = bisectionF(@f_feb15, -2, .1)
[r, iters] = bisectionF('f_feb15', -2, .1)