My son has locked out his phone. It says iphone is disabled what is my next step?

Begin here, https://support.apple.com/en-us/HT204306

If it has just been disabled once, it should give you a time limit. From there, wait out the time limit and re-enter the passcode correctly. If you enter incorrectly, it will disable the iPhone again for a longer period of time.

If you permanently disable the iPhone, or can not get in, plug your device into iTunes and reset the device. This can be done through a backup or set up as a new iPhone.

Start here:

If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support