Unciv! Ever heard of Civ, aka Sid Meier's Civilization? Wanna play it on your phone without shelling out $20 for one of the worst-reviewed mobile ports of all time? Unciv is an open source implementation of a tile-based, turn-based strategy game. Oh, and there's built-in mod support as well. Not huge on mobile gaming, so it's literally the only one I've been playing for months.

Not really a mobile gamer and i either solve riddles on websites or puzzles like sudoku. And I only use open source. I think mindustry and unciv are too complex for a phone game, I like feudal tactics, but it gets stale after some time

I'm hoping you get some solid suggestions. I have such a hard time navigating mobile app stores to find anything that I may want to play

I've only played it on PC and Switch, but Into the Breach is one of my favorite strategy games and the interface is excellent on touch. The randomized campaigns of short turn-based maps is excellent for short play sessions, and has a ton of replayability with a lot of unlockable squads.

Sadly AFAIK it's only available in mobile for Netflix subscribers. But if you are one it's free.

Antiyoy isn't pretty, but it's a great turn based strategy game. Free I think.

To Arms is an odd sort deckbuilder. Free.

Solitairica is like solitaire/fantasy strategy

Rebuild is an older zombie city survival game

Survive is an outdoor survival game. It isn't turn based, but it's not live action either. It's free I think.

Out There isnt strategy in the traditional sense, but you do make decisions and progress further with a little luck and good decisions.

These answers point to a useful pattern: good mobile strategy doesn’t have to be simple, but it does need to tolerate interruption. Unciv removes real-time pressure, Into the Breach preserves a run cleanly, Landrule compresses a full match, and Arknights keeps stages short. So the better test may be: how quickly can you return to one meaningful decision after unlocking your phone? That seems more useful than judging by genre alone.

Not tower defense, but I've been a long time fan of a super simple game caked Landrule. It's literally just Risk, but it's super simplified graphics means it can run on a potato, and the visual information is super easy to digest. It has a ton of speed options so when your comfortable with it, you can crank it up and play an entire game against 5 computer opponents or more in 5 minutes. And, best of all, a tooooon of maps so you can mix it up and keep it fresh.

Arknights is a gacha tower defence that was originally made for mobile clients (in fact, it's only getting official PC client later this month).

In terms of gameplay, I enjoy that most levels are short by the standards of tower defence, so I can get 2-3 new stage clears in a 30 minute session, usually (provided I've actually figured out the strategy). There is some passive progression but it won't give you all the upgrades you need and there is space for optimization and decision making in resource management.

While gacha monetisation model is an understandable turn-off for a lot of people, the difficulty balance allows even fully free-to-play accounts to keep up with the levels and the rates are the most player friendly in my experience.