my phone space is now 28.3gb but if i charge it or leave it idle for a few hours or the next day it goes up to 28.8gb why does this happen and is there anyway to stop this from happening
I assume you're talking about how much storage is being used, correct? Various apps (especially browsers) will build up their cache or data storage over time with normal usage. You generally don't have to do anything about this, unless you happen to have a low-spec phone that only has 32 GB of internal storage.
Half a GB is a drop in the bucket for you, then. Don't get overly concerned about fluctuations in storage, since there's a fair amount of dynamic change going on with cached data.