This is the 1358th most frequent Japanese word.
スマ
"スマ" refers to the Japanese mackerel or commonly the spotted mackerel (Grammatorcynus bilineatus), a type of fish.
In this sentence, 'スマ' refers to a type of mackerel fish, and its usage is as a noun referring to the specific fish species.
スマを食べたことがありません。
I have never eaten a mackerel.
'スマホ' is an abbreviated form of 'スマートフォン' (smartphone). In this sentence, 'スマ' acts as the prefix, commonly used to refer to smart devices.
新しいスマホを買いました。
I bought a new smartphone.
Here, 'スマート' is used as an adjective meaning 'smart' or 'stylish'. The original root 'スマ' contributes to the meaning of sophistication and modern style.