This happens because the UI font size multiplier is set to "Largest" (Settings / Display / Font Size), and device pixel density set to low, "Large" (Settings / Display / Display Size), but the layout of the in-call dialpad was not properly configured to acommodate for this functionality.
I suggest you contacting the local support detailing the screens that have such overrun text. Since it is possible to configure the font size this way, built-in applications should support this properly.
