Again, you are confusing the frame size, measured in pixels, inches, mm, picas etc., with the linked photo size, always in pixels. If you change your default document measurements, your info panel will change. It will show the frame size in, say, mm, and also show the effective ppi of the image, which won't change uless you resize the photo.
As a default , when you place a photo, it will come in at its natural (native) resolution and size. Only by resizing in InDesign will that change. Resizing can be done several ways, using object styles or dragging a frame as you place, for instance. The ideal workflow is to know what size the frame will be in the final document and size the photo in Photoshop before placing it. This eliminates any on-the-fly resampling by either InDesign or the final printing drivers (RIP).
As to your specific question on pixelation, the ppi in the links/info panel should give you a guide. The underlying photo might in fact have pixelization that has nothing to do with placing it here. You may simply have a bad photo. That aside, go by the links/info panel information and confirm it if you like by setting the High Quality Display (Ctrl-Alt-H) and zooming into Actual size (Ctrl-1) and actually looking at the photo. Any pixelization will be apparent.