The one thing that can help the most is to make sure that you prepare ahead of time, and one way you can do this is to search online for common job interview questions and write down an answer for each of these questions. This is a very useful exercise that can help you to be as prepared as possible for any questions that might be asked, and it can also serve as a handy reference sheet for your phone call. You may not be allowed to have notes in front of you for a physical interview, but you can always have this information in front of you while you are talking on the phone.
Another thing that is obviously very important is punctuality. If you are given a certain day and time that you will be receiving a phone call for your initial interview, make sure that you do not sleep in too late so that you are not taking this phone call right after you roll out of bed. And if you are supposed to make the call at a certain time, make sure that you are right on time or even a few minutes early.
Put yourself in the position of the employer or manager that you might end up working for: Doing an interview over the phone is a cheap and easy way to see whether you are a job candidate that is worth investing more time and money into. If you can tell over the phone that a potential job applicant is obviously not informed or qualified enough for the job position, you can save yourself time in the future by telling them right away that this is not the right job for them.
On the other hand, if your phone call makes you sound smart, responsible, and well-informed, this can make your employer feel confident about meeting you in person to see if you are right for the job. This is why it is important to master the phone interview, so use a land line phone instead of a cell phone for a clear connection, make sure that you will not have any distractions going on in the background, be prepared ahead of time, and you can greatly increase your chances of getting your dream job.