Put that phone away. Using your phone or fidgeting with it while listening is not only off-putting but also reeks of disrespect for your interlocutor.
Repeat their last few words
It's common to get lost in the middleof a conversation. In such cases, at least repeat the last few words of the speaker back to them. It makes the other person feel heard.
Offer nonverbal cues
Nonverbal cues like making eye contact, nodding on affirmation, and having an attentive body posture signal you are listening.
Admit shortcomings
If you zoned out in the middle of the conversation, acknowledge that yougot lost and didn't quite get it, and ask them to repeat themselves instead of pretending to understand.
Ask more questions
Asking more questions not only makes the other person feel listened to but also helps you fully get their message. This also ensures that you don't overlook important details.