Excel does not display the leading + sign entered by users, similarly the leading zeros are also not recoganised by excel. However custom formating trick can help you do this. Refer to the following table, where in Phone number 9971112814 has been formated differently to display different formats for the same cell contents.
91 is country code for India, you can change it to whatever code you want to display the number accordingly.
|+91 0000000000||+91 9971112814|
|0091 0000000000||0091 9971112814|