Phone cameras won't give you near the quality you need for Stock photography. If you're serious about photography, start saving for an entry-level digital camera that has a 20 megapixel sensor.
A decent new or used camera + lenses + accessories will range from USD $500 to $2,000. NOTE: A higher price doesn't always mean superior equipment. Read reviews, talk to experts.
As an example, Panasonic Lumix G95 Hybrid Mirrorless Camera with 12-60mm Lens with Accessory Kit for $697. Budget for an additional lens, memory card & cleaning kit. Eventually, you'll want to get a tripod, too.
https://www.bhphotovideo.com/c/product/1739016-REG/panasonic_lumix_g95_hybrid_mirrorless.html
Hope that helps.
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