What did they think of Greek philosophy and reason?

Clement of Alexandria c. 150–c. 215 ADStromata 1.5.28

Philosophy was a schoolmaster to bring the Greek mind to Christ, as the law brought the Hebrews. So philosophy prepares the way for one who is made perfect by Christ.

The Alexandrian view.

Tertullian c. 155–c. 220 ADPrescription against Heretics 7.9–13

What has Athens to do with Jerusalem? What has the Academy to do with the Church? What have heretics to do with Christians? Our teaching comes from the porch of Solomon, who himself taught that the Lord must be sought in simplicity of heart. Away with those who have produced a Stoic, Platonic and dialectical Christianity! We have no need of curiosity after Christ Jesus, nor of inquiry after the gospel.

Tertullian's target is philosophy as the source of heresy. He himself used Stoic ideas freely.

Origen of Alexandria c. 185–c. 254 ADLetter to Gregory (Philocalia 13) 2

And perhaps something like this is hinted at in what is written in Exodus in God's name, that the sons of Israel should be told to ask from their neighbours and fellow lodgers vessels of silver and gold and clothing, so that, by spoiling the Egyptians, they might find material for making the things taken over for the worship of God. For from what the sons of Israel spoiled from the Egyptians were made the things in the Holy of Holies: the ark with its cover, and the cherubim, and the mercy seat, and the golden jar in which the manna, the angels' bread, was kept.

Origen writes to his pupil Gregory, the future Gregory Thaumaturgus, urging him to take from Greek philosophy whatever can serve as general education or preparation for Christianity, as geometry and astronomy serve the reading of Scripture (section 1 of the letter). The Egyptians' gold is his warrant; his warning follows at once (section 3): few take Egypt's useful things and leave, but many, like Hadad the Edomite, end by making a golden calf. The letter is kept as chapter 13 of the Philocalia and printed in Migne PG 11; the text here is the Khazarzar witness, fetched because the library's Philocalia section holds only the letter's opening.

Augustine of Hippo 354–430 ADOn Christian Doctrine 2.40.60

If those who are called philosophers, especially the Platonists, have said anything true and in harmony with our faith, we should not fear it, but claim it for our use from them as from unjust owners. For as the Egyptians had not only idols and heavy burdens, which the people of Israel hated and fled, but also vessels and ornaments of gold and silver and clothing, which that people, leaving Egypt, took for themselves for a better use, by God's command ... so all the teachings of the Gentiles have not only false and superstitious inventions ... but also liberal disciplines more suited to the service of truth.

"Spoiling the Egyptians": the image Origen had used before (Letter to Gregory).