blood streaked mucus phylegm - please help.

Hi, my dad uses oxygen at night and he used to have dry throat as a result. When he gets up in the morning he used to cough a lot to clear his throat as he used to say the mucus builds up in the back of his throat. When he used to cough so much he used to get blood in his mucus/phylegm. He used to say that is the only time he used to get that. However, yesterday around 3:30pm he went to just spit without a cough and he had blood in his mucus. He says he spit three times and all three had blood. Then stopped after 3 spits. He tried to cough and see if he would get blood in his mucus and he didn't. He is not the type that complains but he made this comment about his spit and it got me worried. He doesn't cough blood in the morning anymore is what I'm assuming as he wasn't using the oxygen for the past few months and he recenlty started using it after they added a bottle water to the machine. Any idea what it could be? Please help. He has heart problems. Blood pressure. Other than that he is okay. He is in his early 60s. Thank you. Best Regards.