Your quotes come from the Oxford Textbook of Medicine: Infection, and relate to rhinoviruses (the common cold). You should include context like that in your question, since it will help provide better answers. Your second quote is slightly wrong: it should say recognized, not recognizes.
Pathogens (disease-causing agents) typically follow one of two "strategies":
- Spread slowly, but possibly cause great damage to the host. Example: HIV is spread only by blood or sexual contact, and even sexual contact with an infected partner has maybe a 1% probability of transmission.
- Spread widely, but usually cause just a nuisance to the host. Examples: the common cold and herpes.
Viruses that spread rapidly and kill the host quickly, such as Ebola, tend to be not very successful, since they often extinguish themselves when all available hosts in an area die.
"Mild community infections" probably refers to the second strategy: much of the population is infected, but the infection is not that harmful.
A serotype is a strain of pathogens, identified by their surface proteins. A phylogenetic tree is a diagram that plots how species diverged evolutionarily.
More than 150 serotypes of rhinoviruses were recognized phylogenetically clustered into groups A, B, and C means that the 150+ strains can be mostly grouped into three families based on the similarities of their surface proteins. Based on those similarities, virologists would reconstruct the evolutionary tree, and on that tree you would see three clusters.