When the thrust mode is SPEED, the thrust is controlling the speed.
If the pitch mode is V/S, the elevators are following the selected the rate of climb or descent.
Similarly, if the pitch mode is G/S, the elevators are following the GlideSlope.
If the pitch mode is ALT, the elevators are maintaining the selected altitude.
So, the only time that the elevators control the pitch to follow a selected/managed speed, is Open Climb/Descent, SRS, CLB, and DES (idle path), and in those cases the thrust will be in THR mode (climb or idle).