Not sure if you did a phone update recently but if you did that update to the phone may be causing the problem.

Now first thing I would do is check the connection settings on the phone. Make sure its set to auto connect to your wifi network.

Now if that is ok, I would turn off your modem, wireless router,cell phone, and any other device connected to your home wifi. turn the modem on after a few minutes and let it boot up completely, then do the same for the wireless router, your phone,and the rest of the devices on your home network. See if that fixes your connection situation.

You might also check for a firmware update for the router and your modem. Its always good to be up to date.

Also set the phone to only update over wifi and not cellular data. it will save you money in the long haul.

Good Luck