In any position a player can phrase, but in audiences perspective it may not be conceived what a player phrasing. In this issue posture and concentration is so important.
Posture is mostly thought as a visual item. But it is more than that. Posture should be used as a tool to play more attractive. For example; a player should be relaxed and comfortable. If he posed naturally then this reflects to his phrasing. But if he is nervous and uncomfortable then it will not be Okayed by audiences.
Posture should be correct the body should not be unshaped. It should be agile and reflections should be awaked. It is important that chest stands more forward and little bit looks at down. Two legs are equally stands and players should feel two feet holds the floor. If there is something prevent a player should get rid of it. In some techniques like Alexander Technique down and up parts of your body should be very relaxed like you will fell down but middle part of your body is very strict. In this technique it seems you use only needed part of your body. But, what I think is reflection is a mirror how you think so, some behavior could not be act consciously. But in an exception if players could use bodies consciously, more simplicity they will get. In this time what they are phrasing will be clearer, accepted by audiences and the sound will be always forward. What technique I call Active Playing.
Unlike a player could phrase using his or her body, then all the player, audience and accompanied players will not be encouraged. So, wrong phrasing, technique even anxiety comes minds. Player may obstacle himself own by own. This occurs when a player do not feel himself ready, when he is not relax or nervous. Also, lack of self-confidence is a big obstacle for a player. If players have any of those obstacles then they could first define the problem. Then they can solve trough it. Getting more information, knowledge what they are doing gets them wise in a speech or performing. Thinking and planning the concert or a performing gets them ready. Practicing much and in different places, time gets the anxiety controlled.
Briefly when a player is strict and decisive the less anxiety he has and more successful performing he has. He also controls his body and posture. Posture should be used as a tool to transfer the emotions and his music from inside to outside. Being active in playing makes a commenter more understandable.