Hello.
Are you sure that your mobile phone has a RS232 peripheral? Most modern mobile phones have only USB connection.
If it had, check the voltage levels for each one, maybe the phone uses less voltage than PIC.
I don't have time to check the program right now, but make sure it doesn't have a infinite loop somewhere, maybe near the "if" that checks the button status.
What model of mobile phone are you using? Maybe some users know how to control different models.