Does the phrase "with a team" imply that the speaker is on the team, or rather that the speaker is explicitly not on the team (of course it may also be ambiguous)?
The sentence fragment, "with a team," does not give sufficient indication as to whether the speaker is on the team or not. In this case you are right to say that it may be ambiguous, but mostly due to the lack of context you provided. To say that one "works with a team" would indicate that they are not really on the team, perhaps in a management role. On the other hand, to say that one "plays with a team" would suggest that they are on the team. Could you provide a broader context for your question?