Take a look at this flow:
Anyway, the number of blocks will stack up when the first flow is calling the second flow. i.e. the blocks are 4 in the example.
If you want to keep below the limit, u'll have to be creative. Previously i saw a tutorial that teaches how to do this. in short, u need a orchestrator that is very lightweight, and flow 1 will pass the variables to the orchestrator (and flow 1 finishes). The orchestrator then pass the variables to flow 2 (which is then started).
The process will look something like this: flow1 -> orchestrator, flow 1 stops -> flow 2, orchestrator stops. The challenge comes in that you will have to figure out how to start flow 1 again, assuming that is where everything starts from.
Honestly, it's a pain in the ass to achieve with the 30 blocks limit. I have the same setup, where I have a phone without google play installed. So, I just make my flows very simple and use the phone simply.