Obtain a container of medical disinfectant wipes and wipe down all surfaces of the phone for at least 2 minutes. (Clorox Healthcare Hydrogen Peroxide Cleaner Disinfectant Wipes would be one example). These wipes are in a round container, perforated and pull out through the top. Sometimes the wipes are over-saturated so I use a paper towel to absorb the excess liquid as it could be possible to damage a mobile phone if this liquid got inside.
Isopropyl alcohol on a paper towel or cloth would be an alternative to prepackaged wipes. A mix of water and bleach is an option but I don't know what the best ratio would be for this mix. I would Google the recommended length of time for application of disinfectant as it varies for what is used ie hydrogen peroxide, isopropyl alcohol, bleach mix etc.