- preg_match: documentation ( source)
- array_slice: documentation ( source)
<?php
$input = 'https://someurl.com "This is a \"quote\" in the caption"';
list($url, $caption)=(preg_match('~(\S+) "(.+)"~', $input, $out) ? array_slice($out,1) : ['','']);
echo "url: $url\ncaption: $caption";