Can i catch a cold or flu by masturbating after touching things that have such virus? (e.g. my phone, backpack, wallet, etc after coming home.)

How done ?: You catch these illnesses by passing the germs to your face/mouth from contaminated fingers or by inhaling airborne droplets with the germs. The germs do not enter through your skin. How you masturbate has no obvious connection to how these germs are acquired. Good regular hand washing is one of the best ways of avoiding these illnesses.