HI NMA
I think it's worth taking the opinion of your supervisor, particularly if they have experience on a journal editorial board to see whether they think your submission was broadly of a good enough standard that it might have a chance to be accepted (i.e. the reviewer may just be having an ego trip with a PhD student's work, and being unnecessarily harsh), or otherwise establish with your supervisor what steps you need to take to write to the appropriate standard for journal submission. If your PhD supervisor is not an experienced journal editor then try to get advice from a sympathetic senior member of your department who has experience on a journal.