Here is a simple illustration of how PhaseRep works.
A patient has right-sided headache which ascends from the occiput and settles over the right eye. In addition, he tells you that he is a barber, divorced since 5 years, and tell you how he has a child who has a serious disease and has to spend a lot of money on his treatment. He may relate a strong craving for tapioca chips and sweets. There may be many other symptoms and dreams.
When you enter data into PhaseRep, it is likely that you will enter 'right-sided', 'headache', and 'upwards'. Almost irrespective of the rest of the history, PhaseRep would ask you questions for Silica and Sanguinaria. Let us suppose it asks "profuse, foul smelling footsweat" for Silica. Would you choose it, even if the patient did not have it?
If the patient does not have keynotes of a drug, it will be eliminated from the final analysis, or will get a very low rank.
The other symptoms in the case would lead to other drugs, and their keynotes will also be asked. For example, in the same case above, you might have also entered 'monetary', 'anxious', 'cr sweets'. The program will ask keynotes for other drugs too. But it will certainly ask for Sang and Sil – so you cannot get so lost in the story the patient narrates, that you lose a drug which has consistently produced a very peculiar and typical type of headache.
In addition, PhaseRep will give you suggestions for drugs based on peculiar combinations. If the patient has 'constipation', 'fear or fright' and 'sleepiness' as three symptoms, it may directly suggest Opium in the "suggested remedies" section. Here, there is no cross-checking by presenting keynotes. It just draws your attention to an unusual combination. You can study it in the Materia Medica.
Needless to say, this is a super-simplification of how the program works, but certain things should be evident.
One needs to use PhaseRep often to understand how it actually works. One simple exercise for users would be to think of a drug – say pulsatilla. Now in PhaseRep, choose some rubrics which you are likely to find in a "Puls" patient. Choose some other rubrics also, to confuse the case! Now see the rubrics in the second phase. You will find pulsatilla keynotes being asked for confirmation. Try this for many drugs.