Question asked in phd application form - How you intend to fund your studies
For PhD studies in the UK, funding and admission to the program are usually separate steps. Funding opportunities will generally marked explicitly as such, and many of them are only available to UK/EU citizens resident in the country. If you are just applying for admission to a PhD program, there is an expectation that funding is taken care of separately.

The "ideal" answer for such the question regarding the funding source in a UK PhD application takes the form "I have been awarded the following competetive scholarship which will cover all my funding requirements". Other good typical cases are "My employer (company or government agency) really wants me to do a PhD and will foot the bill". These answers strengthen the application, because they show that someone else is sufficiently convinced of the whole PhD thingie to put a significant amount of money behind it.

"Neutral" answers are "I/my parents are rich and we can just afford this" or "I'm getting student loan from XY". Be prepared to provide evidence of claims like this! These answers mean that funding is taken care of, but don't add to the application beyond that.

"I'll get a part-time job" is NOT a good answer. University regulations typically restrict how much work PhD students are allowed to do, and with that number of hours it is probably not even feasible to cover cost of living, not to mention university fees. Anyone who needs a student visa to come to the UK is subject to even stricter regulation, which will actually be enforced. For the universities, the rationale is that PhD students who spend a lot of time working for a living, and a lot of energy worrying about how to make ends meet are far more likely to underperform or even fail than PhD students focused on research.