It is definitely possible to start earning money online using your phone. Having a good smartphone and a great internet connection enables you to tap into several online earning opportunities.
Most of the online earning sites have been made to be mobile friendly and so you can easily join and start earning.
The first is paid to post forums. Legit ones right now include; beer money forum, Bizdustry, Trendri, Lumoexchange, post bucks and referral index forum.
You could also do blogging from your phone. Just choose a niche, create a blog and start posting blog posts.
Lastly, I can recommend cryptocurrency trading. Especially in a site like Binance which is mobile friendly.