Use separate SSIDs on the router and on the phone delete (forget) the 5GHz network.

@Lwalker11 

thanks. the problem is the 2.4 G network does not always showup in my list of available networks

Any idea. how to keep it showing up?

Thanks

Most times it is the 5 GHz that does not always show up as its range is shorter. In the router WIFI settings, you can try using specific channels and different band width. You may be getting some interference on the channels from things that are not even WIFI such as cordless phones, weather stations, wireless cameras, ... Different devices like different band width.

thanks I will try to stay away from other gadgets which use wifi

The 2.4 is used by many devices other than WIFI. Signals in the WIFI band range are limited in power to help prevent interference however it still occurs. The bands are more of a line of sight much like a TV signal. The futher you are from the signal the slower your WIFI will be. They are also affected by objects such as walls, ovens, and electrical devices so that is why router placement is important. Moving a router even a few feet, higher or lower, turning one way or another, and antenna placement makes a difference. Foe example, I moved my router about three feet and it allowed me to get a 5 GHz WIFI in one of my bedrooms where before I could not get it as a brick chimney blocked it.