I was on good terms with my PhD supervisor throughout my studies. After graduation, I gave a talk at a symposium and my PhD supervisor was in the audience. I was planning to add a few sentences of appreciation to my supervisor during my talk, but decided not to (in order to prevent potential awkwardness). After ruminating about the talk, I also noticed that I perhaps took too much credit ("I developed this assay in the past" etc.) and never credited my supervisor once throughout the talk (must have been subconscious, because I don't know why I didn't in hindsight). All of that is true: I developed the experiments on my own and performed them on my own. However, my supervisor has been indispensable when it comes to "meta-knowledge," general guidance and feedback. Overall he seems like one of the nicest professors in our department, so I felt bad. After my talk, he just left the symposium without saying anything to me. Maybe he was in a rush, but I remember he had done it another time in the past, where he was unsatisfied with my performance on a previous talk. Right after the talk, I sent him an appreciation email with candour, but I didn't receive a reply. Over my entire studies, I can only recall a single email of mine that he had ignored. My friend tells me that he was likely busy with travels, but I think it's very likely that he is disappointed for the aforementioned reasons (or another reason I'm not aware of).
I now need a letter of recommendation from him for my next position. I'm confused on what mode of communication I should opt for (email, phone, in-person) and what content should be communicated. Although in-person seems like the best option, I don't think he is rarely in his office and I live far away now. We are both somewhat socially awkward and averse to awkward tension, so I also feel like a phone conversation might not the right approach. Regarding the content: If I'm apologetic, he might not respond out of awkwardness. There's also the small chance that I'm imagining his anger. If it's just a canned or standard request email, and he is indeed angry at me, he may ignore it or, in the worst - admittedly unlikely - case sabotage the letter of recommendation.
What mode and content is likely to lead to the best outcome in this situation?