<img src = "[[+tv.img:phpthumbof=`w=180&h=150`]]">
This construction returns image with original size
I think that the way you are attempting to use it could be the issue, you can either try:
<img src = "[[!phpthumbof? &input=`[[+tv.img]]` &options=`&w=180&h=150`]]">
Or change your TV output type to "image" then:
[[+tv.img:phpthumbof=`w=180&h=150`]]
Should work.
I think what might be happening is that your TV output is just the path & phpthumbof can't do anything with just the path it needs the actual image as input ~ so it's just getting ignored.