Explanation

When you view dashboards in portrait mode on a phone, you notice the dashboard tiles are laid out one after another, all the same size. In the Power BI service, you can create a customized view of a dashboard, specifically for portrait mode on phones.
Step 1: Open the Dashboard.
Step 2: Change the dashboard view to Phone view
Step 3: Pin items from the reports to the dashboard.
Step 4: Rearrange, resize, or remote items from the Phone view.
Create a phone view of a dashboard
1. In the Power BI service, open a dashboard (Step 1)
2. Select the arrow next to Web view in the upper-right corner > select Phone view. (Step 2)

The phone dashboard edit view opens. Here you can unpin, resize, and rearrange tiles to fit the phone view.
The web version of the dashboard doesn't change.
3. Select a tile to drag, resize, or unpin it. You notice the other tiles move out of the way as you drag a tile.
The unpinned tiles go in the Unpinned tiles pane, where they stay unless you add them back.
4. If you change your mind, select Reset tiles to put them back in the size and order they were before.
5. When you're satisfied with the phone dashboard layout, select the arrow next to Phone view in the upper-right corner > select Web view.
Power BI saves the phone layout automatically.
Reference:
https://docs.microsoft.com/en-us/power-bi/create-reports/service-create-dashboard-mobile-phone-view