Here I am going to briefly go over the potential tell tale sings that a phone job inter interview went good.
The obvious factor with phone interviews is that you can't judge how the interview is going by checking the body language of the interviewer as you are on the phone. So the only real way you can tell if the phone interview went good is through 'what they are actually saying', 'how they say it' and your 'general gut feeling'.
So what have they actually said to you?
One sign that could indicate that the phone interview is going good, is if the interviewer starts asking you personal questions about how you can go about being hired with questions such as "what time can you meet the team?" or "what steps do you need to take in order to depart from your current job?". Both these questions show genuine personal interest in you and are steps that you would need to take in order to eventually get hired by them.
Another potential sign is if the interview is trying to sell the company and business to you, instead of you asking questions s/he is trying to convince you further that this is the job for you. Telling you about potential perks that you may get, clear career ladder, how the business is growing and has potential etc.
Different people, have different opinions on this matter, but how long has the interview gone on for? I believe personally speaking, the longer the interview has gone on for, the more likely the interview has gone well, as why would someone want to waste their time carrying on with someone who doesn't think they have what it takes.
How are they saying it?
As the only form contact you have is verbal, another important sign is to indicate the tone of voice they are using and then trying to decipher it. Generally speaking I believe if they gradually start speaking towards a higher and higher pitch, towards the end of the interview, this is a good indicator to show that they are interested in you. Due to this indicating that this could express that they are excited about the possibility of hiring you and it kind of offers a 'vulnerable' side to them. This is however, my own opinion and hasn't been scientifically proven, just my general experience.
Also notice the pace change, if the speed increases ever so slightly, this is probably another good indicator as to tell if your phone interview is going well. Again, an increase in speed could indicate that they are again subconsciously excited about hiring you and want to get things moving faster, again my own opinion to a sign that the phone interview went good.
General Gut Feeling?
This is probably the best indicator to go on to really assess if the interview went well, if you feel that you engaged with the interviewer, applied knowledge of your own and research that you have conducted to questions etc. You felt that you answered questions politely and generally carried out most the points I made in telephone interviews: questions and answers, the more likely you have actually done well.
Although bear in mind that the following sings, may not actually correspond to the success of whether you get the job or go through to the next round of interviews i.e they could be misleading. There is also the possibility that you did indeed perform well in the phone interview, but other people may have simply performed better or were more suited to the job on offer. If you feel that this might be the case, it would be a good idea to send an email or ring them back asking for some feedback on your interview so you can improve for the future.
If you feel that you need to improve on the performance of your telephone interviews, there is only two really ways of going about this. Practice, as they practice makes perfect - have more and more phone interviews and also try reading up on methods to better your interview performance, personally I would start reading up on the fantastic books Ron Fry has produced: one hundred smart questions to ask on your interview and one hundred and one great answers to the toughest interview questions both containing really great strategies and tips on approaching any sort of interview.