The most common and most likely answer to this crossword clue is the 6 letter word FROGGY
I've seen this crossword clue in The Guardian
F
R
O
G
G
Y
More clues leading to the result FROGGY
Buddy explains!

The straight part
We know that "Like amphibian" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case like amphibian = froggy.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FROGGY mean?
FROGGY noun- A frog.
- A Frenchman.
- Froglike.
- Suffering from a frog in one's throat; hoarse.
- Inclined to fight; aggressive.
- Energetic or strong.