Once you get past the pronunciation of phở ("fuh" instead of "foe"), the next question might be, why the obsession with numbers? What does the delicious Vietnamese brothy soup (with rice noodles, bean sprouts, lime, heaps of cilantro, and usually some meat strips) have to do with numbers? This thread over on Reddit.com clears it up:
Oftentimes they're lucky numbers. "In some Asian cultures, eight is associated with wealth or prosperity. Repetition is considered desirable (Olympics started 8/8/08). Or to mark a date in Vietnamese history, or the owners' personal life." For example, Phở 67 could stand for 1967, the year the owner fled Vietnam during the war. The Phở 75s of the world are probably honoring 1975, the year Saigon fell.