John Chrysostom

"That ye receive her in the Lord, as becometh saints. (Gr. "the saints.") That is, for the Lord's sake, that she may enjoy honor among you. For he that receives a person for the Lord's sake, though it be no great one that he receives, yet receives him with attention. But when it is a saint, consider what attention he ought to have shown him. And this is why he adds, "as becometh saints," as such persons ought to be received. …

Homily on Romans 30 ↗

Theophylact of Ohrid

That is, show her honor for the Lord's sake. He who receives even an insignificant person for the Lord's sake shows honor to the Lord; and Phoebe was a saint: consequently, all the more was it fitting to show her honor. Therefore he added: "as befits the saints," that is, as one ought to receive the saints. That is, supply what you can, lend a helping hand; for he did not say: satisfy all her needs. …

Commentary on Romans ↗

Thomas Aquinas

Then he mentions two things he wants done for her, the first of which is that she be honorably received. And this is what he says: that you receive her in the Lord, i.e., for the love of God, as befits the saints, i.e., according as it is fitting to receive saints, for it says in Matthew: he who receives a just man because he is a just man shall receive a just man's reward (Matt 10:41). Instead of as befits the saints, some books have worthily enough, i.e., fittingly; but those texts do not agree with the Greek. …

Commentary on Romans ↗