Half the battle is knowing the conference exists. The other half is everything else. If you only learn about venues from your advisor's offhand comments, you're working with a sample size of one tired professor.
Here's the thing people get backwards. A conference deadline tracker app on iOS won't discover venues for you. That's not its job. Its job starts once you know the name. For discovery you want venue matcher SaaS territory: tools that take your topic, your keywords, your past references, and return venues worth comparing. The phone app is the companion piece, the thing that turns a discovered venue into a tracked deadline with alerts.
Compare iOS options on three things. Discipline coverage first. A beautiful app tracking engineering conferences is decoration if you're in the humanities. Alert quality second: customizable lead times beat fixed ones, because thirty days out means something different for a workshop and a flagship. Third, the boring metadata: locations, submission links, notification policies, all the stuff you'd otherwise hunt through three websites to find.
My contrarian take: the app matters less than the database behind it. A mediocre app fed by a great academic venue finder beats a gorgeous app with stale data every time. Data goes stale fast in this game. Check when the venue list was last updated before you trust the alerts. I mean it. Check the date.
A mobile app for academic submission deadlines pairs well with a real academic conference deadline tracker that keeps dates, locations, and submission links current. Use the matcher to find venues, the app to make sure you don't miss them.
And when the manuscript is ready, confjournal.fyi runs paper formatting and submission checks for whichever venue you picked.