If you have a 7260-00 telephone then you have a DX-80 or possibly a DX-120 system. Both systems have a nice feature called External Call Forward. What you ask can also be setup in the voicemail (if you have it) with installer help.
Unless your installer disabled it on your extension, you should be able to set an ECF right from your phone, and simply enter your cell phone number as the destination. Check your Extension User Guide if you need help doing this. The system will then call your cellphone using another line when a call comes into your phone on the ringing line.
By the way, welcome to the board!