Arabic is Egypt's official language, and Egyptian Arabic specifically is the everyday spoken dialect. English is widely spoken across the tourism industry, though — hotels, cruise ships, guides, and most restaurants and shops in tourist areas operate comfortably in English, so language is rarely a real barrier for visitors.
Why guides in particular are reliable
Guides are typically fluent in English (and often additional languages), since that's a core part of the license required to work as a tour guide in Egypt — see What Does a Nile Cruise Egyptologist Guide Actually Do? — which is part of why a guided cruise or tour feels manageable for first-time visitors.
A handful of Arabic phrases — hello, please, thank you, and basic numbers for bargaining — are appreciated and useful outside the most tourist-focused settings, but they're a nice-to-have rather than a necessity for getting around comfortably.