Ok, another dumb question ... a DB exist for this installation correct? Maybe, it's not accepting or can find 'defaults' for those prompts that I see you've left blank ... I know it's a pain, but fill them in with the defaults shown.
It must have already created a config.php file if you are at the step of entering an admin user. Did it not? Or at that step it's trying to create a config.php file - which, BTW, would take attributes of ownership by the user executing php install.php.
Could try this ... there is a config-dist.php file in the moodle folder that contains lines one could add to config.php to turn on debugging at that level. Errors then, would be reported to the screen ... hopefully.
So stop at creating that user ... add those lines ... and using a different browser (if using FireFox, use Safari or something else) hit the site to see if it re-cognizes it hasn't finished installation and goes forward. We might see something in the errors reported that gives a clue.
One could also, build a config.php file from what one sees in the config-dist.php file. Rename config.php to config.php.old. Copy the config-dist.php file to config.php (set permissions where it's readable by apache user/group), edit it ... filing in whatever info needed ... DB, DB User, DB password, etc..
Then use browser to hit site.
'spirit of sharing'. Ken