The two are connected through webhooks and via this mechanism I send data from my phone to Homey and vice versa.
For instance, I have a flow which let me know when there’s movement upstairs. But when my children are going to bed I want to disable this flow temporarily. On my phone I have a Tasker task with which I can disable this flow with one press of a button. The Tasker task flips a variable in Homey.
Another example: I have several Google Nest speakers placed in my house. I have a Tasker task that, when I activate it, asks me where I want my voice command to be broadcasted. When I choose one, my phone asks me for my voice command and the text from this command will be sent to Homey via webhook, the appropriate flow will pick it up and the text will be broadcasted by the app Google Services on the selected Google Nest speaker.
So, many ways available to give Homey your user input for flows.