A phantom is like a ghost. I’ll bet you’ve heard of the famous musical “Phantom of the Opera.”
A fathom is a measurement of depth in water. It’s equal to about 6 feet or 1.8 meters.
“The shipwreck sits on the ocean floor at 2000 fathoms.”
Fathom is also a verb that means to understand. “I just can’t fathom why you left your job.”
A phantom is an image that only appears on the mind that is only heard and sensed with no physical manifestation like a ghost or an apparition.
"Legend has it that an evil phantom haunts the house down the street."
Fathom means to measure the length, depth, capacity, scope of something. It also refers to the ability to understand or comprehend an idea.
"I still can't fathom how you intend to execute this project."