Just to make sure you know: ppi means pixels per inch.
Let's pretend we have an image which is 300×300 px. Its resolution is set to 150 ppi.
Then we make a duplicate of that image and set the resolution to 300 ppi (without resizing it).
These two images are exactly the same! They contain the same amount of pixels, the same information. Only difference is the resolution.
The resolution set in Photoshop is only a setting to tell other applications what the intended resolution is. It tells nothing about the image. It could be set to anything you like.
When you place an image in InDesign by clicking once (not dragging) the image will be placed at the resolution saved in the image.
So a 300×300 px image with the resolution set to 150 ppi will get the width:
300 px / 150 ppi = 2 inches
150 pixels are printed for each inch and since the image is 300 pixels wide the physical width of the image becomes 2 inches.
If we place the duplicated image (still 300×300 px but with the resolution set to 300 ppi) the width will be:
300 px / 300 ppi = 1 inch
It's the same image, but here 300 pixels are printed for each inch, so the image has higher resolution, but therefore also smaller physical size.
In InDesign you can select an image and in the Info Panel or the Links Panel you can see the Actual ppi and Effective ppi of that image (you might need to change the settings of each panel to get that info).
The Actual ppi is just the resolution saved in the image. Remember this is only a setting and has no real meaning.
The Effective ppi is the interesting one. This tells you which resolution the image has at the physical size you have chosen for it in your document. Always use this value to check if your images has the resolution you want for this particular print.