Its going to be slow ... maybe that's not a problem though (e.g. one-off or small data set (including in the future!!)
Storing the Employees.E_Mobile with the space already removed (in a separate field, if you need the current "human readable form" as well ) would be quicker.
If the job at hand is always to ignore the country-code prefix then either separate that into two fields, or if there is also a need to compare "trailing matches" then perhaps store the REVERSE value? and compare that. Using LIKE 'xxx' + '%' is much faster (if indexes available) than LIKE '%' + 'xxx' (but i'm sure you know all that ...)