Your question is somewhat broad as i in person don't know the mobile number format you would like to validate. Thing is, mobile number formats differ from country to country.
Either way, go here and search for your country mobile number "regex":
http://regexlib.com/Search.aspx?k=mobile%20number[
^]
I already performed a generalised search for you on the link above but care to tailor the search your way.
Happy coding,
Morgs