I dont play many mobile games, usually just something to pass the time in the elevator at work or something like that. So I dont know of many strategy games or rather any good games at all on mobile platforms besides elder signs omens. Im probably about to commit blasphemy in peoples eyes here but when I give recommendations I do so for games that Ive played, liked, and know are good. That said, if you want strategy games that are pretty complex I think you would be better off getting yourself a decent laptop or desktop PC and then going for one of the grand strategy games published by Paradox. Games like Europa Universalis 4, Crusader kings 2, or even hearts of iron 4 if you like something more modern (by modern I mean ww1 and ww2). However grand strategy games are extremely complex and can take hundreds of hours to play.
Some lesser strategy titles to think about include Dungeon keeper 2, Civilization 5, Age of wonders 3, Age of empires 2, X-com: Enemy unknown, FTL, Frozen Synapse, Fate of the world,
Then there are the 4x strategy games (my personal favorite sub genre). Good ones include Master of orion 2 (very old but still one of my favorites), Stardrive, Sins of a solar empire (which has a really cool star trek mod in...I think it was beta last I heard), and Endless space
Theres also a variety of Real time strategy games. Some good ones include Dawn of war 2, Starcraft, starcraft 2, and Warcraft 3
Im probably forgetting a ton of other strategy games but I think thats a big enough list for you to do some research and find out if they're for you or not.
