var strdata = "MobileP: 9712899082P: 123654789FaxG: 0265123456EmailG: abc@gmail.com";
var values = strdata.Split(new string[]{"MobileP: ", "P: ", "FaxG: ", "EmailG: "},
System.StringSplitOptions.RemoveEmptyEntries).ToArray();
now you can use the values as below
var MobileP = values[0];
var P = values[1];
var FaxG = values[2];
var EmailG = values[3];