Certainly phone, as you long as you sound like a trustworthy person. In that sense, an accent or poor English can be a minus. You don't need to lead the conversation or have sales skills - it would take exceptional sales skills to cold-call someone and sell them a domain they don't have an interest in.
The advantages of phone:
1-Unlike email, you are sure that someone has gotten your message.
2-Unlike email, you can ask for the decision makers and usually get through to them.
3-If you are well-spoken, you can give the buyer a sense of trust and reliability, rather than come off as a sleazy squatter trying to hustle money. (This should be number 1)
4-You will often get your interested or not interested response right away.
5-You can make a personal connection with the buyer that may lead to more domain purchases.
Disadvantages of phone:
1-Time. You'll waste a lot of it. You can email 100 people in an instant. Calling them will take all day.
2-Money. You'll waste some of this too. Emails are free.
3-(If you're not well spoken, or your English is poor), you'll turn people off and lose potential sales.
4-No record. Sometimes old emails get a second look by potential buyers.
5-No record. There might be a misunderstanding and you'll have nothing to support your interpretation.
6-You might say (or agree to) something stupid.
Unless you are selling a more valuable domain, the calls may not be worth your time. But, in my experience, personal contact is way more effective in both buying and selling. Don't try to sell the name. Tell the person it's for sale, and ask if they would like you to send details by email. Then follow up later. Simple as that.