Does anyone know how to forward an office phone to a cell phone?

It depends on what type of phone system and phone are at the office. It’s different for each one. At very least the person needs to provide the type of make/model of the phone.

Well, I know his cell phone is an iphone. lol.

If the office phone is part of a PBX, then your friend has to get it programmed by the systems administrator at the office, if at all the feature is available.

If it is a stand alone phone line in your friend’s office, then the phone company’s call forwarding service can be activated to get the job done.

I would caution against doing this on your own as many companies forbid the practice