You can consider doing a part-time PhD that can be completed any time between 4 and 7 years (actual times may vary). This is an option provided for people with external responsibilities, such as having a full-time job. It is certainly feasible, but it includes the supervisor and the department agreeing. Also, the situation around fees and funding needs to be clarified, as the department may hesitate to provide funding to a part-time student with a full-time job and allocate it instead to a full-time PhD student with no other means. You might still be able to secure paid work (teaching or marking), a stipend/ bursary or for fees to be waived or covered by something else. This, of course is country and department specific. Technically, combining a full-time job and a part-time PhD is doable.
That said, even a part-time PhD requires a significant time commitment provided continuously, or at least in specific productive periods doing the PhD. In brief, research is a strange beast that cares little for your personal circumstances and cannot be put easily in boxes or timetables. It requires clarity of thought, calmness, time (often time to waste!) and personal commitment, which the conditions might not provide despite your best efforts. Even if the goal is not an academic career but simply completing a PhD, the demands are still high and you need to consider how to balance work, further responsibilities (social life, family, caring etc) and possible changes in the future (e.g. moving away, starting a family). I dare compare it to someone like a fencing or chess champion: a high level athlete, with all the dedication that demands, who cannot support oneself from that activity and needs to put as much time and effort in a full-time job. It is not a leisure hobby or a past-time activity. I do not know how you imagine research to be, and everyone has a different story according to their field, personality and circumstances. The more stories you hear, the better.
The advice I give to anyone is to think very carefully about the reasons for starting a PhD. Such a commitment is not undertaken because "there is nothing else to do", "I want to be a student again/more", "all my friends have one" or "I want to be a Doctor". It is a very demanding, long endeavour, unlike most experiences and requires a clear, persistent and strong personal desire and motive. I am not trying to dissuade or indirectly criticise you, and have no reason to doubt your composure, personality or abilities. I am only emphasising the need for careful thought, because quite early on, and after the first experience, you will need to decide what level of quality you will be able/ willing to reach in your work. The level of quality greatly depends on what I discussed earlier, so it becomes a virtuous or vicious cycle. At the end of the day, nobody knows your conditions better than yourself and you are the ultimate judge on how to combine the two.