iCloud messages huge compared to phone

Hi,

my iCloud is full because I have 75gb of messages backed up but when I check the size of messages on my phone is says 1.52gb.

if I delete the message backup will it remove them off my phone?

im guessing it has saved back ups from previous phones. Earlier this year I went through my phone to delete large attachments so it must be saved under previous devices.

cheers

Nic