Ok, so 2 things contributing to that.
1. Your phong tag has Use Edge Breaks active.
2. In the text object your caps / bevels have the phong break rounding box enabled, which it is by default.
Disabling either of those should remove the dividing line between beveled cap and rest of mesh. However, does tend to lead to messy results on the corners of the bevels, as we see below, so mostly it is preferable to leave that on.
A messy, non phong-breaked corner, earlier.
You'll notice on that particular text object that adjacent topology changes as it goes round the corner, and this is only cleaned up (ie cut / truncated) by the solve intersections checkbox, which we also need here for beveled caps to work in most circumstances. I would agree it is perhaps not the most elegant of solutions, but it is what it is in order to give easy access functionality all within 1 single object, which is rather what the Text Object is all about ! We should be able to circumvent some of these problems by using a bevel deformer instead, where we get more control, but again I fear that geo mismatch at the corners may lead to rounding artefacts anyway, despite the better control / ability to only apply it to certain edges / and manual phong break advantages.
OR at any point you can make the mesh editable, and then manually select the edges you don't want phong broken and then use / unbreak phong shading command (I get it from down the very bottom of the right click menu) to remove that hard edge specifically without affecting the corner ones...
It probably is worth noting that if we use the 3rd option in the text object rounding department - bevel outside - that actually solves the corner phong beak scrappiness because no geo is intersecting badly like it was before, at the expense of slighty 'fatter' text !
And then, if you set your phong tag angle to something low like 18 degrees, you can get the best of both words, thusly...
But then of course we have this massive discrepancy between rounded bevel phong shading and the razor sharp edge running back away from the caps, and a fairly grim transition between the 2 on that corner...
So lastly, the phong tag itself can help us there. By setting the angle in there waaay high instead, and changing the phong type to something like Angle and Area weighted we can improve it again, and gain consistency of shading in the bevel AND back across the mesh, so I guess this is the ideal solution in your case.
We can see this better if we zoom out a bit and look at the 'B'... very nice consistent shading everywhere.
CBR