Phone Number missing Leading Zero??

Hi All,

I am working on a 2016 organisation and I have noticed that each telephone number in the system is missing the leading zero. The field used to capture the telephone number is OOTB:

For example mobile numbers are appearing like - 7712345678 and they should appear - 07712345678.

Is there a way to fix this? Do you think this is a format issue?

Thanks in Advance.