It is possible. The cellphone manufactures say no. Some animal studies say yes. We may never know. It is hard to do a study on human gonads (any volunteers?). To be safe, carry it in a holster on your hip.
While serious. People are looking into the association of cell phones, "electromagnetic waves spectrum", and brain tumors, it makes little intuitive sense. First, the incidence of brain tumors has not changed since the proliferation of cell phones post 1995; radio waves and internal radiation from the handhelds are of low energy, ergo skin doses would be high, and no increase in ear pinna skin cancer. Crotch?