Formal:
* Puis-je parler à... ? (Formal, most common) - This is the most neutral and polite way to ask.
* Pourrais-je parler à... ? (Formal, slightly more polite) - This is even more polite than "Puis-je parler à...".
* J'aimerais parler à... (Formal, slightly less direct) - This means "I would like to speak with..." and is slightly less direct than the first two options.
Informal:
* Je peux parler à... ? (Informal) - This is a more casual way to ask, but still polite.
* Est-ce que je peux parler à... ? (Informal) - This is another casual way to ask, but slightly less direct than "Je peux parler à...".
Example:
* Puis-je parler à Madame Dubois, s'il vous plaît? (May I speak with Mrs. Dubois, please?) - Formal
* Je peux parler à Antoine? (Can I speak with Antoine?) - Informal
Remember to choose the appropriate phrase depending on who you are speaking to and the context of the conversation.