DUI breath tests are legal without a warrant in Vista and throught the United States. The U.S. Supreme Court ruled that a breath test is minimally intrusive and needed in DUI cases, therefore it is not an illegal search and seizure. However, blood tests are much more intrusive and require a warrant if a person refuses to take a blood test. If there are exigent circumstances a warrant may not be required. That depends on the individual case, like if there is difficulty in getting a warrant in a timely manner because of other circumstances like medical treatment, combative defendant or some other basis.
Cell phone searches without a warrant are unreasonble searches and illegal. Anything found in that search may not be used against the person arrested. However, if there is sufficient information to get a warrant to search the contents of the phone, then it may be searched. There are also possible exigent circumstances that may justify the cell phone searches without a warrant, like officer safety or destruction of evidence.
DUI contacts and arrests come from multiple sources. The most common reason for the initial contact is the traffic or equipment violations, but there are several other reasons also like accidents, citiizen calls, checkpoints and stops made while investigating other crimes.