Lady Scarlet wanted to conceal evidence. She knew that things were headed there when she had a bitter argument with her husband. So she threw her phone in anger and then she crushed it and acted as if it was the anger making her do it but she was doing it to hide evidence of some wrong she had done and did not want her husband to confirm by checking his phone.
Lady Scarlet found some texts between her and other girls and she was filled with rage as she did not understand why he did it. She was not going to let him get away with it and so she took his phone and she crushed it then she asked him to explain why he had done it. Once he had looked at the way she had treated his phone, he told her what she needed to know.