What Jesus was warning about
In Matthew 6, Jesus addressed people who chose prominent public places for prayer because they wanted an audience. The problem was not their volume or location by itself. It was the desire to be seen as spiritual. Jesus says they had already received the reward they were seeking, human approval, rather than looking to their Father (Matthew 6:5).
That warning still reaches us. A prayer can be spoken beautifully in a church gathering and be sincere. It can also be quiet and private yet filled with a desire to feel superior. God sees beneath both the words and the setting.
But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly.
Jesus himself prayed aloud
Jesus sometimes prayed where others could hear him. At Lazarus's tomb, he spoke to the Father before calling Lazarus out of the grave. He explained that he prayed aloud because of the people standing nearby, so that they might believe the Father had sent him (John 11:41-42). His prayer was not a performance. It pointed people towards God.
On the cross, Jesus also cried out to the Father in the hearing of those around him (Matthew 27:46). Spoken prayer, then, is not less genuine or less humble. Its purpose matters.
Then they took away the stone from the place where the dead was laid. And Jesus lifted up his eyes, and said, Father, I thank thee that thou hast heard me. And I knew that thou hearest me always: but because of the people which stand by I said it, that they may believe that thou hast sent me.
Prayer can be silent or spoken
Scripture makes room for quiet prayer. Hannah prayed with moving lips, but without an audible voice, as she poured out her grief before the Lord (1 Samuel 1:13, 1 Samuel 1:15). God heard her. You do not need the right volume, eloquence, or setting for God to receive you.
At other times, speaking aloud can help. It may help you focus when you are distracted, give shape to a burden you cannot sort out internally, or let another Christian join you in prayer. God knows what we need before we ask, yet Jesus still invites us to ask our Father (Matthew 6:8).
Praying with other people
The first Christians prayed together audibly. After Peter and John were released, the believers lifted their voices to God as one community, asking for courage to keep speaking about Jesus (Acts 4:24, Acts 4:29-31). Shared prayer was part of their life together, not something Jesus had forbidden.
So pray aloud if it helps you seek God, whether you are by yourself, with family, or gathered with a church. Keep it simple and truthful. If you are invited to pray publicly, you do not need impressive phrases. Speak to God, not to the room. And when silent prayer is all you can manage, that is still prayer.