"Ac 1750" is not a model number. Look for "Model" on the product label.
> [...] I installed the phone app [...]
_Which_ "the phone app"?
> [...] now my phones [...]
Not a very detailed description of those devices.
> [...] are not connecting to my router.
A clear description of what does happen would be more useful than a vague description of what does not happen. As usual, showing actual actions (commands) with their actual results (error messages, LED indicators, ...) can be more helpful than vague descriptions or interpretations.
What about other devices?
Visit http://netgear.com/support , put in your (actual) model number, and look for Documentation. Get the User Manual (at least). Read. Look for the LED descriptions and "Troubleshoot". Pay particular attention to something like the "WiFi On/Off button with LED" or "WiFi LED". Did you press it? Further reading might not hurt, either.
