mobile speed differences can often just mean that on mobile i'ts on a slower connection (do you have slowness on mobile while on WIfi or only while on normal cell data?)
I would check to make sure that your images are optimized, you don't want it to take multiple megabytes to load a page while on mobile.
Next see how many requests are being made. Check the marketplace for the resource combiners so you can combine all your CSS and Javascript calls into 1 call, that can help speed things up since a browser can only have 5 open downloads at a time per domain, so if you have 100 requests it can take a bit.
Lastly is a mobile phone can have less memory and processing power, which can be hurt by a lot of javascript, but this is rarely the case.