A clause can only be interrogative; a phrase can only be declarative.

Phrases are concerned with grammar; clauses are concerned with lexis.

A clause is a larger unit that contains its own verb; a phrase may not contain a verb and is a smaller constituent unit.

A phrase acts as a subject; a clause acts as an object.

-wise

-ly

-wards

a-

writes (present) vs. wrote (past) vs. will write (future).

tells (non-continuous) vs. is telling (continuous).

tells (present) vs. told (past) and will tell (future).

loves (active) vs. is loved (passive).

Numerus duplex

Opposemes

Singularia tantum

Pluralia tantum

Its written form.

Its meaning or content.

Its morphemic segmentation.

Its oral (spoken) form.

They are replaced by a compound numeral from the next decimal base.

They are always placed after the noun they modify.

They do not take the plural form.

They are always written with a hyphen when used in a compound numeral.

It possesses stable right-hand connections and variable left-hand connections.

It connects a noun (or noun equivalent) with a word from almost any other part of speech.

It connects two similar syntactic units, such as words of a similar type or clauses.

It connects words in speech but is completely devoid of lexical meaning.

Lexico-grammatical meaning of "relations (of substances)" and function as a linking word indicating syntactic relations.

Lexico-grammatical meaning of "substance" and function as a subject/object.

Lexico-grammatical meaning of "action/process" and function as a predicate.

Lexico-grammatical meaning of "quality" and function as an attribute.

It is often avoided by writers of formal English. 

It is a rule that applies only in regional varieties of English. 

It is a rule that is most likely to apply in particular circumstances.

It is a rule that applies universally and without exception.

Finite verbs (finites) and non-finite verbs (verbids); the indicative, conditional (subjunctive), and imperative

Notional verbs and semi-notional verbs; the infinitive, gerund, and participle.

Standard verbs and non-standard verbs; the indicative, conditional (subjunctive), and imperative.

Transitive verbs and intransitive verbs; the indicative, conditional (subjunctive), and imperative.