It sounds like you're navigating a tough situation. The decision to suggest a break in the relationship was likely a response to feeling uncertain and possibly hurt by the changes you've observed in her behavior. Based on what you've shared, here are some points to consider:

Communication Method: The main concern your girlfriend seems to have is the method of communication. A voice message might have felt impersonal to her, especially if you were both expecting a more direct conversation. It's understandable that she might have been taken aback by hearing such an important message in this format rather than through a face-to-face conversation or at least a phone/video call. In situations like this, direct communication often helps both parties feel heard and understood.
Her Doubts: Her expressed uncertainty about the future is understandably concerning, especially with your clear long-term plans to move abroad. It’s important to know if her feelings are due to the uncertainty of the future or if something has shifted in her feelings toward the relationship. The fact that she mentioned wanting to stay friends even if you break up suggests she might value the relationship but is struggling with where it’s headed.
Trust Issues: The change in her behavior, like being protective of her phone and chatting with another guy, is understandably unsettling. While you mentioned there's nothing physical going on, your feelings of discomfort with these changes are valid. It's essential to address these feelings directly with her. Rather than just waiting for her reaction, you could have a conversation that allows both of you to express your concerns and feelings openly, which could provide clarity.
Seeing a Future Together: Your long-term plans are clear, and it’s possible that she’s unsure if she wants to be part of that future or if she has a different vision for herself. This is a significant conversation to have, and it’s important to give her the space to articulate her feelings as well.
Next Steps:
Consider reaching out to her to have a more direct, face-to-face conversation (or at least a phone call). Express your concerns and listen to hers as well. This could help you both understand if you're still on the same page regarding your future.
Address the trust issues by talking about the changes in her behavior. You might find that she is just going through a phase of needing space or that there’s something deeper going on.
Take some time to reflect on what you truly want in the relationship and whether both of you can reconcile your differing views on the future.
Ultimately, the voice message might have been a bit of an overreaction, but it was likely a way for you to express your feelings and gain clarity. The key now is to follow up with an open conversation that allows you both to express your feelings and decide on the next steps.