At least I have learnt something new with all this messing around on the phone.
Just found an MP3 album on my phone which didn't have the TRACK field filled in. All the filenames had track numbers, so they alpha sorted correctly, but no TRACK tag in the MP3. This meant the phone sorted the tracks in Alphabetical order according to the TAGS, ignoring the file names.
Once I filled in the correct TRACK tag field in the MP3s by loading the whole album up into MP3TAG on the PC, the phone then successfully showed the tracks in the correct order.
This is showing how important the tags are to the phone... (and at least I got something from this thread instead of just a headache...)