Should I buy a camera or use my phone?
Use your phone, since it will be with you most often. There is plenty of good free software for combining multiple digital images to obtain better quality and/or wider perspective.
Macro and telephoto images are not easily derived from most smartphone images, but a holder and remote control for your smartphone will add much more bang for the buck than getting involved with DSLRs.
Otherwise, to minimize that "big purchase", Ebay offers used working Canon DSLR bodies, EF 300mm zooms and new 50mm f/1.8 lenses selling less than $200 in total. With tripod, extension tubes, post processing, and patience, these will suffice for telephoto and macrophotography other than sports, wildlife and other fast-moving subjects where multiple exposures are not feasible and the cost issue becomes less avoidable. Other DSLR systems are less generally available so cheaply..
Cell phone cameras are surprisingly capable, but they don't offer the creative range that you can get with a high end system camera.
It takes a commitment to lug one around.
If you don't feel the need for one, you probably don't need one. Save your money.
If you're not sure, borrow one for a few days.
Good luck to you.