Please explain adverb phrases, prepositional phrases, verb phrases, noun phrases and adjective phrases along with examples.

2) "How is the weather today, Sam?" said Jonh.
Why isn't a comma required before "said John?"

Look up and study each kind of phrase here:

http://www.chompchomp.com/terms.htm
The explanations and examples are excellent.

2) There's already a mark of punctuation after "Sam" -- there doesn't need to be a second one.

Adverb phrases, prepositional phrases, verb phrases, noun phrases, and adjective phrases are all types of phrases that add information and detail to the main components of a sentence.

1) Adverb Phrases:
An adverb phrase is a group of words that functions as an adverb, modifying a verb, adjective, or another adverb. It provides additional information about how, when, where, or why the action in the sentence takes place.
Example: She ran quickly to catch the bus.

2) Prepositional Phrases:
A prepositional phrase consists of a preposition and its object, along with any modifiers of the object. It provides information about the relationship between the object of the preposition and another word or phrase in the sentence.
Example: The book is on the table.

3) Verb Phrases:
A verb phrase consists of a main verb and its helping verbs. It expresses the action or state of being in a sentence.
Example: They have been playing soccer all day.

4) Noun Phrases:
A noun phrase is a group of words that functions as a noun in a sentence. It can include a noun and its modifiers or determiners.
Example: The beautiful sunset painted the sky with vibrant colors.

5) Adjective Phrases:
An adjective phrase is a group of words that functions as an adjective, modifying a noun or pronoun. It provides additional information about the noun or pronoun.
Example: The house with the red door is mine.

Now, let's move to your second question.

2) "How is the weather today, Sam?" said John.
The reason a comma isn't required before "said John" is because the dialogue tag ("said John") is an essential part of the sentence. In this example, the dialogue tag is providing important information about who is speaking. If the comma were used, it would indicate a pause in the sentence, suggesting that "said John" is not an integral part of the sentence's meaning. However, in this case, the dialogue tag is necessary for clarity and attribution. Therefore, no comma is needed before "said John."