As Terry already wrote, you can make 2D plots in Prime in two different ways.
Using the chat component enables you to use labels, secondary y-axis, grids, etc. But unfortunately it has it drawbacks, too (badly integrated, very slow, no units, ...)
Using the native plot (as you did) has the advantage that its more natural, faster reacting and can be used with units. But the drawback is that it does not offer things like labels, a secondary y-axis or ... grids.
There have been posted workarounds which add gridlines in the native 2D plots via an additional trace.
E.g.: https://community.ptc.com/t5/Mathcad/In-MCD-Prime-4-0-is-there-any-way-to-add-gridlines-to-plots/m-p/86492/highlight/true#M34243
or https://community.ptc.com/t5/Mathcad/Bode-Plot-NaN-Complex-values-Error-and-Plot-Grid-Does-Not-Exist/m-p/830506/highlight/true#M203237
So give both ways to make 2D plots a try and chose the one most appropriate for you.