Several things:
a) If your goal is to become a professional psychologist, a PhD is not the route you should be aiming to take. You should be aiming to do a DClinPsy/DEdPsy etc as appropriate to the field you want to go into. A PhD prepares you for a career in academic research, not working as a professional psychologist.
b) PhDs are normally funded by research councils or sometimes other funding bodies, this will normally cover the full fees of the PhD plus a yearly tax free stipend which is to support the student's living costs. In a number of fields doing a self-funded PhD (which a doctoral loan would be considered as) is seen with some stigma as the key to an academic career is securing funding for your research, and not getting funding for a PhD is seen as failing the first attempt at doing that. This does vary somewhat and is more prevalent in STEM fields.
c) Usually for full-time PhDs you're expected to be working more or less 9-5 on the PhD. It's a job. It's not like doing an undergrad or even masters degree where you go and do a few hours of lectures, some assignments, and whatever after that. You are being paid to do full time research. Therefore it's usually not possible practically to work during a PhD outside of paid teaching/marking/demonstrating activities within your department. Also I think it's typical for most PhDs to require their PhD candidates to receive approval from the supervisor before seeking external employment, for full time PhDs.
So I think you need to firstly figure out if a PhD is actually the qualification you want/need to get to pursue your goals, and if so you should be looking at funded PhD positions for pre-existing projects or crafting a very strong research proposal and applying for research council funding.