Not Biblical. All we know is that she was a virgin prior to the conception of Jesus Christ. Jesus is not the Father, something Jesus himself makes clear.
LDS doctrine doesn't rely on the Bible alone. Here's all we have in the Bible about the conception of Jesus:
Luke 1:31-1:38
31And now, you will conceive in your womb and bear a son, and you will name him Jesus. 32He will be great, and will be called the Son of the Most High, and the Lord God will give to him the throne of his ancestor David. 33He will reign over the house of Jacob for ever, and of his kingdom there will be no end.’ 34Mary said to the angel, ‘How can this be, since I am a virgin [I do not know a man]?’* 35The angel said to her, ‘The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the child to be born* will be holy; he will be called Son of God. 36And now, your relative Elizabeth in her old age has also conceived a son; and this is the sixth month for her who was said to be barren. 37For nothing will be impossible with God.’ 38Then Mary said, ‘Here am I, the servant of the Lord; let it be with me according to your word.’ Then the angel departed from her.
As to method we don't know any more. We do know that Mary did not have sex with her husband until after Jesus was born.
Matthew 1:25 (New International Version)
25 But he did not consummate their marriage until she gave birth to a son. And he gave him the name Jesus.
That's all we know from the Bible. LDS doctrine teaches differently given additional revelation. Believe as you like, but using the Bible alone you cannot surmise beyond what we have as to method of conception for Jesus. All we know is that she was a virgin prior to conceiving Jesus Christ. She couldn't physically remain one after his birth. Joseph consummates the marriage, no mention is made of her continuing virginity and Jesus has siblings.
No one can believe in just any old being they happen to label as Jesus and expect that that's good enough. Only the virgin born Jesus, who is God Himself, sinless, died, buried and was resurrected, the Jesus of the New Testament, is capable of saving anyone. False Jesus's can't save anyone.
True and I presume you mean Mary started as a virgin as she certainly couldn't be one after Christ's birth.
That said, one doesn't have to believe in the Trinity to be saved. That's a Biblical fact.
LDS doctrine doesn’t rely on the Bible alone
__________________________________________________
But the LORD Jesus Christ who is God does...
The Bible is the only Word of God...
You mean like this?
John 10:24-33 24So the Jews gathered around him and said to him, "How long will you keep us in suspense? If you are the Christ, tell us plainly." 25Jesus answered them, "I told you, and you do not believe. The works that I do in my Father’s name bear witness about me, 26but you do not believe because you are not part of my flock. 27 My sheep hear my voice, and I know them, and they follow me. 28 I give them eternal life, and they will never perish, and no one will snatch them out of my hand. 29My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father’s hand. 30 I and the Father are one."
31 The Jews picked up stones again to stone him. 32Jesus answered them, "I have shown you many good works from the Father; for which of them are you going to stone me?" 33The Jews answered him, "It is not for a good work that we are going to stone you but for blasphemy, because you, being a man, make yourself God."
John 14:8-11 8 Philip said to him, "Lord, show us the Father, and it is enough for us." 9Jesus said to him, "Have I been with you so long, and you still do not know me, Philip? Whoever has seen me has seen the Father. How can you say, 'Show us the Father'? 10Do you not believe that I am in the Father and the Father is in me? The words that I say to you I do not speak on my own authority, but the Father who dwells in me does his works. 11Believe me that I am in the Father and the Father is in me, or else believe on account of the works themselves.
LDS doctrine doesn't rely on the Bible alone.
Therein lies the problem. Adding to Scripture and making things up LDS has wandered away from the truth and followed Satan.
2 Corinthians 11:13-15 13For such men are false apostles, deceitful workmen, disguising themselves as apostles of Christ. 14And no wonder, for even Satan disguises himself as an angel of light. 15So it is no surprise if his servants, also, disguise themselves as servants of righteousness. Their end will correspond to their deeds.
If it were important for us to know, God would ahve told us. Be that as it may, Scripture was fulfilled that a virgin conceive and bring forth a son. If Mary had sex with Elohim as LDS teaches, she wasn't a virgin.