Evans, put into the main draw after No. 7 Radek Stepanek withdrew with a foot injury, defeated third-seeded Philipp Kohlschreiber 6-4, 2-6, 6-4. He saved three break points in the first set and two more in the third.
He only converted two of his eight break chances but those decided the first and third sets for the win.
Phau, No. 358 in the rankings, beat Dudi Sela 6-4, 6-3 by finishing off five of his six break opportunities. Phau hadn't won an ATP main-draw match since last March until this week.
Top-seeded Tommy Haas got by Andrey Kuznetsov in a tight 7-6 (8-6), 6-4. Haas had the only break of the match -- that won him the second set -- and took just seven more (75-68) points in the match than Kuznetsov.
Fifth-seeded Marin Cilic, the defending tournament champion, gained a place in the semis with a 7-5, 6-4 win over No. 4-seeded Ivan Dodig. Cilic had two breaks in each set, which allowed him to take a 3-2 series edge over Dodig.
Phau and Cilic meet in the first semifinal with Evans and Haas following. Phau and Evans are both seeking their first ATP finals appearances.