Why did she refer to Yosef as "ha'Eved ha'Ivri;" whereas, in 39:14, when she spoke to the members of her household, she referred to him as "Ish Ivri"?
Oznayim la'Torah (to 39:14): His title 'Eved' was long forgotten to household. When relating the incident to her husband, she wanted to demean Yosef in his eyes as much as possible.
Divrei David: In both cases, she tried to justify why she let herself be secluded with him. (a) He is an Ish (very distinguished); he is not suspected to venture to sin with me. Also Ivri (from Ever, who was very esteemed) adds to his importance. To her husband, she had a greater defense - (b) A slave would never be so bold as to do so to his master's wife!
Ha'amek Davar (to 39:14,17): She told her household that he came to lie with her (39:14). Whether he is a slave or a free man serving in the house, he is culpable, and the master is culpable for bringing such a man to the house. To Potifar, however, she said "to sport with me;" so she called him an "Eved" - i.e. he should not thus belittle his master's wife! 1
Ha'amek Davar: To the members of the household, she called him an "Ivri" - i.e. their nature is hot (licentious). They have a law of fire ("Esh Das Lamo" - Devarim 33:2) and are brazen like fire. To her husband, she intended, "Ivri" - a brazen nation that does not submit to its master.
Why does it say "Leimor" here; and again below, "when Potifar heard her words, Leimor" (39:19)?
Alshich: He recognized that she fabricated matters, in order that people would believe her words. He was angry at her. To cover her shame, he incarcerated Yosef.
Ohr ha'Chayim: She said that the household can testify like she says. Indeed, Potifar got angry only after he heard them confirm her story.
QUESTIONS ON RASHI
Rashi writes: "'He came to me' - ... to sport with me; this slave that you brought...." What does Rashi explain by changing the order in the Pasuk?
Gur Aryeh: Taken in order, the verse might mean, 'he brought this slave for sport with me' [which is certainly not the verse's intention]. Rashi clarifies how the verse is to be understood.