Rom 2:14
By nature:- By some, this phrase has been supposed to belong to the previous member of the sentence, “who have not the law by nature.” But our translation is the more natural and usual construction. The expression means clearly by the light of conscience and reason, and whatever other helps they may have without revelation. It denotes simply, in that state which is without the revealed will of God. In that condition they had many helps of tradition, conscience, reason, and the observation of the dealings of divine Providence, so that to a considerable extent they knew what was right and what was wrong.

Rom 2:14:-
these having not the law:- the written law
"into written and un written (q): the written law is that which was used in commonwealths; and that κατα εθη γινομενος, "which was according to custom or nature", was called unwritten, such as not to go to market naked, nor to be clothed with women's clothes; which things were not forbidden by any law, but these were not done because forbidden by the unwritten law;'' which he calls "unwritten", because not written on tables, or with ink; otherwise it was written in their minds, and which by nature and use they were accustomed to.
(John Gill)

(q)
Laertii Vit. Philosoph. l. 3. in Vita Platon.