can I record a conversation with my phone when I am speaking to someone on the call. the only voice recorded is mine , and the other persons voice is not recorded. can I legal use this in court
There are laws against recording conversations, which were passed in response to a government practice of listening in on conversations between people. The weaker form of such laws says that at least one party to the conversation must consent to the recording. The stronger law, operative in Washington, California and about a dozen other states, is that all parties to the conversation must consent. The intent behind these laws is to require consent or knowledge of one or all of the people being recorded. What is not entirely clear (in all-party states) is what constitutes a communication, and what a party is, given the wording of the statutes.
Washington law is an example of an all-party consent law, which states a prohibition against recording without "first obtaining the consent of all the participants in the communication". The law does not state this in terms of "the consent of those persons who are recorded". It is unclear whether a person who could in principle hear and be heard (e.g. in a room full of people, with the phone on speaker) are "participants" since the term is not defined. California law refers to "the consent of all parties to a confidential communication", again with no specific mention of people who do not speak, and also no exception made for "parties" who are not actually recorded.
The court in CA has determined that a confidential communication is one in which the parties have a reasonable expectation that no one is listening in. Suppose that A and B are having a quiet conversation in public, and they do not expect that anyone else can hear them, but there are other people nearby. This is a confidential conversation, recording of which requires permission of all parties. A and B can agree to record the conversation. A common sense understanding of "party" would find that if C can actually hear the conversation, he is still not a party to the conversation, therefore he does not have veto power over A & B recording their conversation. To the best of my knowledge, the courts have not ruled on what exactly constitutes a "party" or "participant". Nor have they ruled on what constitutes a "communication". It is possible, but legally untested, that you can record yourself (e.g. with a recorder in the room with you) talking into a phone, where there is some other person on the other end of the line: you're just recording your monologue.
However, the legal utility of doing this is really not obvious, and you really need to hire an attorney who is versed in your jurisdictions case law on the topic, before sticking your head in the noose.