in 2017 phone farming became very popular for earning a passive income. There are basically two types of apps that you can earn from - data collection apps and watching video apps. You won't see a massive income each day and could earn around $0.40 if you live in the US or even Canada. However, this is possible if you live in other parts of the world, you'll just need to choose the apps that target your regions.
If you want to set up a phone farm you should buy up old Android devices and not iOS devices. Furthermore, you should only pay around $15 - 20 for your phone. Look for phones that have 1GB of memory if possible. Make sure the device you buy is unlocked and don't purchase tablets.
The video watching apps will be the major source of your income. However, it is advised to set up all your data collections apps first because they don't require a lot of effort to set them up. Many of the apps will require you to use a phone number when setting up the app. You can use your current phone number or ask to borrow friends phone numbers.
You can use Panel App which is a data collection app and it will accept multiple devices using the same app with the same phone number. You'll earn around $1 a month from the app because you need 1000 views to equal the $1.
Embee Meter CX is another data collection app that you can set up and use. You have other ones and will need to search your location to find the best ones for your area. You can also use Perk TV Live, Perk Pop Quiz, Swagbucks Watch TV, and the list goes on. It is easy to search on Google for apps that work the best in your regions and there are quite a few apps now available for India only. I'd choose these if you want to get started.