To delete all products from your magento store using phpMyadmin. Use following queries to delete all products. Before doing this make sure to backup your existing database. So if anything goes wrong you can import your old database.

Magento Delete All Products

TRUNCATE TABLE 'catalog_product_bundle_option';
TRUNCATE TABLE 'catalog_product_bundle_option_value';
TRUNCATE TABLE 'catalog_product_bundle_selection';
TRUNCATE TABLE 'catalog_product_entity_datetime';
TRUNCATE TABLE 'catalog_product_entity_decimal';
TRUNCATE TABLE 'catalog_product_entity_gallery';
TRUNCATE TABLE 'catalog_product_entity_int';
TRUNCATE TABLE 'catalog_product_entity_media_gallery';
TRUNCATE TABLE 'catalog_product_entity_media_gallery_value';
TRUNCATE TABLE 'catalog_product_entity_text';
TRUNCATE TABLE 'catalog_product_entity_tier_price';
TRUNCATE TABLE 'catalog_product_entity_varchar';
TRUNCATE TABLE 'catalog_product_link';
TRUNCATE TABLE 'catalog_product_link_attribute_decimal';
TRUNCATE TABLE 'catalog_product_link_attribute_int';
TRUNCATE TABLE 'catalog_product_link_attribute_varchar';
TRUNCATE TABLE 'catalog_product_option';    
TRUNCATE TABLE 'catalog_product_option_price';
TRUNCATE TABLE 'catalog_product_option_title';
TRUNCATE TABLE 'catalog_product_option_type_price';
TRUNCATE TABLE 'catalog_product_option_type_title';
TRUNCATE TABLE 'catalog_product_option_type_value';
TRUNCATE TABLE 'catalog_product_super_attribute';
TRUNCATE TABLE 'catalog_product_super_attribute_label';
TRUNCATE TABLE 'catalog_product_super_attribute_pricing';
TRUNCATE TABLE 'catalog_product_super_link';
TRUNCATE TABLE 'catalog_product_enabled_index';
TRUNCATE TABLE 'catalog_product_website';
TRUNCATE TABLE 'catalog_product_entity';
TRUNCATE TABLE 'cataloginventory_stock_item';
TRUNCATE TABLE 'cataloginventory_stock_status';