<?php
$input = 'RequestNo":"595e3931618fa","MobileNo":"9503048769","CardExists":"N","Response":"SUCCESS","Message":"Verification code for your wallet sent on requested Mobile Number.","Code":"300"';
$chunks = array_chunk(preg_split('/(:|,)/', $input), 2);
$result = array_combine(array_column($chunks, 0), array_column($chunks, 1));
print_r($result);