Experts said the reason is that phones are often passed between people which spreads the germs around - but they are never cleaned which means the diseases keep on building up.
Charles Gerba, a microbiologist at the University of Arizona, said during his ongoing experiments he has found that bugs get onto a phone because it is so close to our hands and mouths.
When somebody lets a friend or a stranger use their mobile their bacteria easily gets onto the device too.
Professor Gerba added that because mobiles are electronic some people are reticent about cleaning them, the Daily Mail reported.
While toilets tend to get cleaned frequently, because people associate the bathroom with germs, cellphones and other commonly handled objects - like remote controls - are often left out of the cleaning routine.
