Viruses and germs including the flu virus can live on hard surfaces and phones for up to 24 hours and you can kill the virus and germs on the phone much sooner using some disinfecting wipes which will get rid of the virus and germs.
On fabrics and other porous surfaces viruses and germs live up to 15 minutes.
If you have the flu it's a good idea to wipe down your phone or anything else you touch using disinfecting wipes.
Also if you have the flu you should wash your bedding to kill the flu viruses and germs to keep them from spreading.