2.4 speed problems

For some reason the band width of 2.4 is giving problems of low speed of wifi for no apparent reason. However the 5.o speed is OK Any reason for this and what to do to rectify as my phone cannot receive the 5.0 speed.

There are a number of suggestions here: http://www.makeuseof.com/tag/4-reasons-wi-fi-slow-fix/

The bandwidth of the 2.4 GHz band is about 20 MHz.

A quick fix to try is to set your router to Channel 13 which is rarely used by default.

would a router set at 5.0 band work or connect to a phone which only has 2.4 band?

The router would need to be dual-band. If 5 is not a possibility then you are stuck with the limitations of 2.4. You probably have some local form of interference - Bluetooth, wireless phone, neighbour's router. A little experimentation with channels may help.